The Commonwealth will argue only One Nation senator Malcolm Roberts and former Greens senator Scott Ludlam should be found to have been wrongly elected to Parliament at the last election.

If that argument is successful, the political career of former Greens senator Larissa Waters could be revived just months after her snap resignation.

Senator Roberts, Mr Ludlam and Ms Waters are among seven politicians facing the High Court, after questions were raised about whether their dual citizenship made them ineligible to hold office.

Section 44 of the constitution bans anyone with dual citizenship from being elected to Parliament.

Submissions filed on behalf of Attorney-General George Brandis this afternoon argued the other five politicians, including Deputy Prime Minister Barnaby Joyce, should not be kicked out of Parliament.

The Commonwealth's submissions, written by Solicitor-General Stephen Donaghue, argue the constitution should only be interpreted to disqualify those who have "voluntarily obtained, or retained" foreign citizenship.

It argues a "person who does not know that they are, or ever were, a foreign citizen" should not be ruled ineligible.

That argument goes to the heart of the cases put forward by Mr Joyce, Nationals deputy leader Fiona Nash, former minister Matt Canavan and South Australian senator Nick Xenophon.

All claim they never had any knowledge they could be foreign nationals by descent, and the laws of other countries should not force them out of Parliament.

Ms Waters and former colleague Mr Ludlam already quit Parliament after it was revealed they were dual citizens of Canada and New Zealand, respectively.

Both Ms Waters and Mr Ludlam were born overseas, but Mr Donaghue argued Mr Ludlam knew he was a dual citizen and did not take action to renounce it.

Mr Donaghue said Ms Waters "was not aware that she was or had even been a Canadian citizen" when she nominated for Parliament, which meant she couldn't be expected to renounce her dual citizenship.

Last week, the High Court ruled Senator Roberts was indeed a British citizen at the time of the last election.

Justice Patrick Deane threw out Senator Roberts's arguments that he had only ever believed he was Australian.

Senator Roberts was born to a Welsh father, signed a form as a teenager which stated he was a UK citizen, and had enough concern to contact British authorities to check whether he was a UK citizen before the 2016 election — but still argued he had not breached the constitution.

Door open for Waters return

ABC election analyst Antony Green believes that if the High Court agrees with the Commonwealth's arguments, it could leave the door open for Ms Waters to return to Parliament immediately.

In that case, because Ms Waters would not have been in breach of the constitution at the time of the election, a recount of the Queensland Senate votes would not be needed.

As she already resigned from Parliament, the Queensland Greens could nominate her to replace herself — and ask Queensland State Parliament to ratify her return to Canberra.